1. Field of the Invention
The present invention relates to racks used to hold work-in-progress in microchip fabrication laboratories. More particularly, the present invention relates to a collapsible version of such a rack that can be folded out of the way in order to facilitate maintenance on laboratory equipment located in close proximity to the rack.
2. Description of Related Art
Microchip fabrication laboratories must be kept clean and must be isolated from exterior environments to prevent atmospheric particulates and other impurities from contaminating wafers as they are produced. Contamination can result in performance degradation and decreased reliability. Because of strict environmental control requirements, space is often at a premium in these "clean" laboratories. As a result, storage locations for work-in-progress must be collocated with process equipment and both must be tightly arranged to conserve limited space.
The microchip fabrication process consists of three basic operations: layering, patterning, and doping. In the layering process, thin layers of different materials are grown on, or added to, the wafer surface. Portions of these thin layers are selectively removed to form desired circuit patterns. Dopants are then used to change the conductivity characteristics and resistivity of selected regions in the wafer surface.
The actual number of steps the wafer goes through will vary with the type and complexity of the circuit being constructed. There are several variations on each of the basic operations described above and each variation is designed to achieve a somewhat different result. By iteratively layering, patterning, and doping the surface of the wafer, complex integrated circuits can be produced.
During the normal course of the fabrication process, wafers must be stored on work-in-progress racks. To prevent contamination and to avoid costly transportation requirements, these work-in-progress racks must be located in the same clean rooms as the process equipment. A typical fabrication laboratory consists of tightly packed process equipment with work-in-progress racks located next to each workstation.
In the past, stationary racks have been used to store work-in-progress. These stationary racks are the type often found in medical laboratories. They have four legs and stand on the ground. They are made of oxidation-resistant stainless steel and thereby minimize the risk of particulate contamination. Under ideal operating conditions the stationary work-in-progress racks effectively perform their function. However, operating conditions are rarely ideal.
The sophisticated process equipment used in microchip fabrication periodically requires maintenance. In a typical fabrication laboratory with thirty-six etchers, there will always be a few units down for maintenance. Much of this equipment requires side-panel or back-panel access for maintenance activities. Because of the tightly packed configurations in a clean room, access is restricted by the presence of work-in-progress racks.
When a piece of process equipment requires maintenance, the adjacent stationary work-in-progress racks must be moved to provide adequate access to the equipment. Since a loaded rack could be holding millions of dollars worth of products, and since racks may tip when being relocated, loaded racks are virtually always unloaded prior to being moved. A problem is caused by the limited space in the clean laboratory. When a stationary work-in-progress rack is moved, it will still take up valuable space. If only one work-in-progress rack must be moved, space can usually be found for it. Frequently, however, multiple units will be down for maintenance and several racks will be displaced at the same time. Some of them must inevitably be moved to inconvenient locations such as in walkways or in front of doors.
Based upon the foregoing, it should be understood and appreciated that prior art racks used to hold work-in-progress in microchip fabrication laboratories have a number of shortcomings and deficiencies.